WRRCTR No.189 Geology and hydrogeology of the island of Pohnpei, Federated States of Micronesia

dc.contributor.author Spengler, Steven R. en_US
dc.contributor.author Peterson, Frank L. en_US
dc.contributor.author Mink, John F. en_US
dc.date.accessioned 2008-07-17T22:31:11Z
dc.date.available 2008-07-17T22:31:11Z
dc.date.issued 1991-03 en_US
dc.description.abstract The island of Pohnpei is the eroded remnant of a large shield volcano that was built up from the surrounding sea floor by the repeated eruption of mildly alkalic lava. The main island is composed entirely of volcanic material erupted episodically over the last 9 million yr. The volcanic construction of Pohnpei can be divided into three stages-of activity. The first was a shield-building phase dominated by the frequent eruption of alkali olivine basalt, which was followed after an eruptive hiatus of roughly 1.5 million yr by sporadic volcanic activity dominated by basanitic and hawaiitic composition lavas (Awak volcanic stage). Shortly after the end of the shield-building stage, a large-scale landslide event is postulated to have removed much of the northwestern portion of the original shield volcano. The final stage of volcanic activity (Kupwuriso volcanic stage) produced voluminous flows of undersaturated lavas, which blanketed much of the southern half of the island. The thick, massive, low-permeability post-shield-building lavas of the Awak and Kupwuriso volcanic stages dominate the present-day geomorphology and hydrogeology of the island. Due to regional subsidence and sea-level rise (roughly 5.5 m over the last 6,000 yr), Pohnpei lacks extensive coastal plains of sedimentary material around its perimeter. Instead, volcanic rock and fringing mangrove swamps occur along the coastline around much of the island. Rainfall on the island is abundant year-round and ranges from 400 cm/yr along the coastline to an estimated high of 900 cm/yr in the island's interior. A high runoff-rainfall ratio (0.67) is estimated for the island's river basins. An evapotranspiration rate of 140 cm/yr is estimated for the island. These values lead to an estimated islandwide groundwater recharge of 600 to 750 million liters per day. Groundwater development on Pohnpei has been limited mainly to areas in the northern part of the island in and around the town of Kolonia and Palikir, the new Federated States of Micronesia capital site. Wells in the Kolonia area exploit local unconformities between flow units of the late-stage volcanics and the unconformity between these volcanics and the underlying shield-building lavas. Somewhat more productive wells located in the Palikir area exploit relatively unweathered shield-building lavas. Groundwater development in the northern half of the island is hindered by the low permeability of the basement rock and by the lack of an extensive, low permeability capping layer to impede the movement of basal groundwater out into the lagoon. More favorable conditions for the development of basal groundwater are thought to exist in the southern half of the island due to the presence of relatively thick deposits of low-permeability ash near the coast, although groundwater has not yet been developed there. en_US
dc.description.sponsorship U.S. Department of the Interior, Geological Survey Grant/Contract No. B-249 en_US
dc.format.extent ix + 79 pages en_US
dc.identifier.citation Spengler SR, Peterson FL, Mink JF. 1991. Geology and hydrogeology of the island of Pohnpei, Federated States of Micronesia. Honolulu (HI): Water Resources Research Center, University of Hawaii at Manoa. WRRC technical report, 189. en_US
dc.identifier.uri http://hdl.handle.net/10125/1977
dc.language.iso en-US en_US
dc.publisher Water Resources Research Center, University of Hawaii at Manoa en_US
dc.relation.ispartofseries WRRC Technical Report en_US
dc.relation.ispartofseries 189 en_US
dc.subject hydrogeology en_US
dc.subject geologic mapping en_US
dc.subject groundwater en_US
dc.subject geochemistry en_US
dc.subject gravity en_US
dc.subject dikes en_US
dc.subject rainfall-runoff relationships en_US
dc.subject evapotranspiration en_US
dc.subject Pohnpei en_US
dc.subject Ponape en_US
dc.subject Eastern Caroline Islands en_US
dc.subject.lcsh Geology -- Micronesia (Federated States) -- Pohnpei Island. en_US
dc.subject.lcsh Groundwater -- Micronesia (Federated States) -- Pohnpei Island. en_US
dc.subject.lcsh Hydrogeology -- Micronesia (Federated States) -- Pohnpei Island. en_US
dc.title WRRCTR No.189 Geology and hydrogeology of the island of Pohnpei, Federated States of Micronesia en_US
dc.type Report en_US
dc.type.dcmi Text en_US
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